1. Field of the Invention
The present invention relates to a recording apparatus in which a carriage is controlled by means of a linear encoder.
2. Related Background Art
In general, a printer checks the presence of a printing sheet by a sheet sensor in response to a print instruction, and, in the presence of the printing sheet, feeds the printing sheet to a printing position by driving a platen with a line-feed motor. Subsequently, a printing operation is effected by reciprocating a printing head with a carriage motor in a lateral direction, and, prior to the printing operation, a home position sensor detects that the printing head is at a home position.
FIG. 1 shows such a home position sensor 4 and its relation with a linear-encoder 5 having slits as shown in FIG. 2.
Light emitted by light-emitting diodes 30 is transmitted to phototransistors 32 through the linear encoder 5 and a light-receiving slit 31 to generate a signal corresponding to the slits 5-1 of the linear encoder. The signal is supplied as a feedback signal to a carriage motor 8, and is also utilized as a print timing signal for a printing head 2. Another signal corresponding to slits 5-2 of the linear encoder 5 is used for defining the printing range in the displacement of the carriage.
In contrast to the linear encoder 5 of FIG. 2, requiring two sets of light-emitting diodes and phototransistors, there has also been proposed, in the Japanese Patent Application Laid-open No. 65308/1985, a control method utilizing only one series of slits as shown in FIG. 3. In such method, the linear encoder 5 has slits up to broken-lined positions whereby the movement of a carriage 8 takes place as indicated by chain lines. In this method, the carriage is reversed always after it returns to the home position. Consequently, the moving range of the carriage is considerably larger than the printing range b, and there is required a long time for reversing the carriage.
In order to avoid the above-mentioned drawbacks, it is known to reduce the number of slits to solid slits shown in FIG. 3, by eliminating the slits in the broken-lined area, thus shortening the reversing ranges for the carriage 8. In FIG. 3 b indicates the printing range, while a and c indicate reversing ranges for the carriage 8. This method allows shortening of the reversing time of the carriage, but, in a first line in which the carriage 8 starts from the home position 50, the carriage exceeds a predetermined speed vl as indicated by a curve 51, so that the carriage speed reaches a value above a servo control range when the carriage enters the printing range.
Such excessively high speed gives rise to a shorter interval of ink emission, in the case of an ink jet printer, which ink jet recording head may not be able to respond to, or gives rise to other failures of the apparatus.